When you are pulled over by a police officer and the officer suspects that you have been drinking, the officer will most likely ask that you submit to a series of roadside field tests. While an officer can request that you preform a variety of different test, there are only three tests that have been recognized by the National Highway Traffic Safety Administration (NHTSA) for the use of detecting impairment The three Standardized Field Sobriety Tests (SFST) recognized by NHTSA for detecting impairment (i.e. drunk drivers) are: the Horizontal Gaze Nystagmus Test (“HGN”), the Walk and Turn Test, and the One Leg Stand Test. According to the NHTSA, the three recognized road-side sobriety tests are only reliable when “the tests are administered in the prescribed standardized way,” and none of the test elements are changed.
Horizontal Gaze Nystagmus is an involuntary jerking of the eyes as they move from side to side. The HGN test is an eye test where the officer has a driver follow a stimulus (usually a pen or finger held twelve to fifteen inches from the subject’s face) with their eyes. The subject is instructed to keep the subject’s head still and follow the stimulus with his or her eyes only while the officer makes several “passes” with the stimulus. As the stimulus is moved horizontally across the subject’s field of vision, the officer looks for certain “clues” in the subject’s eyes. The officer is looking for three different clues in each eye, for a total of six possible clues: lack of smooth pursuit, distinct and sustained nystagmus at maximum deviation, and onset of nystagmus prior to forty-five degrees. Four out of six is considered a fail.
The Walk and Turn Test involves having a subject walk a straight line with nine heel-to-toe steps, turn, and take nine steps back. The test begins by putting the subject in a heel-to-toe “instructional” position while the officer explains and demonstrates the test. When the instruction is complete the officer has the subject perform the “walking stage” of the test. The officer is looking for eight impairment clues during the test, including: starting the test too soon, failing to maintain the instructional position, taking the wrong number of steps, raising the arms more than six inches from the sides, missing heel to toe contact by more than half of an inch, stepping off line, making an improper turn, or stopping walking during the test. Two out of eight is considered a fail.
The third test is the One Leg Stand. For this test, the officer has the subject raise one of his or her legs out in front of them with the foot approximately six inches from the ground. Both of the subject’s legs should be kept straight and the sole of the raised foot should be parallel with the ground. The subject’s eyes should be focused on the raised foot during the test. The subject then counts out loud, “One thousand and one, one thousand and two,” until told to stop. The officer times the test for thirty seconds. The officer watches for four clues on the one leg stand test, including: hopping, putting down their foot, swaying, and raising the arms more than six inches from the sides. Two out of four is considered a fail.